In vitro cell culture is the complex process by which cells are grown under controlled conditions, generally outside of their natural environment but as close to their natural in vivo conditions as possible. In practice cell culture refers to the culturing of cells derived from multi-cellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi, insects and microbes, including viruses, bacteria and protista.
In vitro cell culture provides material necessary for research and application in pharmacology, physiology, and toxicology. This includes bioprocessing and cell therapy where cell cultures are necessary.
Cells are grown and maintained at an appropriate temperature and gas mixture in a cell incubator. Typically, mammalian cells are incubated at 37° C. with a pH maintained between 7.2 and 7.4. The pH is typically controlled using a bicarbonate buffering system in the medium, in conjunction with an incubator atmosphere of approximately 5-7% carbon dioxide by volume. The carbon dioxide reacts with the water to form carbonic acid which in turn interacts with bicarbonate ions in the medium to form a buffering system which maintains the pH near physiological levels. Oxygen is essential for cellular metabolism and growth. Culture conditions can vary for each cell type, and variation of conditions for a particular cell type can result in different phenotypes.
A variety of cell types are grown in culture including connective tissue cells, skeletal, cardiac, epithelial cells, neural cells, endocrine cells, immune cells, lymphocytes, melanocytes, and many types of tumor cells. Similarly a variety of media are available depending on the particular growth requirements of the cells and the growth conditions.
Commercially available gas permeable cell culture bags are currently a standard device format used for cell culture. Cell culture bags that are constructed with gas permeable films advantageously provide a large surface area for gas exchange while maintaining a closed system. Disposables also helps reduce the risk of contamination for the cell culture and for the environment.
Cell culture bags are commercially available from OriGen Biomedical Group (OriGen PermaLife™ Bags), Baxter (Lifecell® X-Fold™ related to U.S. Pat. Nos. 4,829,002, 4,937,194, 5,935,847, 6,297,046 B1), Medtronic (Si-Culture™, U.S. Pat. No. 5,686,304), Biovectra (VectraCell™), and American Fluoroseal (VueLife™ Culture Bag System, covered by U.S. Pat. Nos. 4,847,462 and 4,945,203).
Gas permeable films should be selected based on a variety of characteristics including gas permeability, moisture vapor transmission, capacity to be altered for desired cell interaction with cells, optical clarity, physical strength, and the like. A wide variety of information exists that describe the types of gas permeable materials that have been successfully used for cell culture.
Among various kinds of rubbery materials, silicone rubbers are preferable in most cases in respect of their electric properties, low cost, precision moldability and durability in repeated bending and releasing movements.
Silicone films for cell culture bags have high oxygen permeability, good optical clarity, good resistance to puncture, typically do not bind cells, and can be easily fabricated into a wide variety of shapes. Silicone films may be less than about 3 mm, about 2 mm, about 1 mm, or about 0.8 mm in the surface areas where gas transfer is desired. The best selection of material depends on the application.
Fluoropolymer films have desirable characteristics that make them a popular choice for culture bags. Compared to silicone, fluoropolymer films are more biologically, chemically and immunologically inert, as well as being hydrophobic. Fluoropolymer films like FEP (fluorinated ethylene-propylene) do not trigger immune responses in immune cells and progenitor immune cells. However fluoropolymer films are more expensive, less gas permeable then silicone films, and are difficult to adhere to other polymers.
Therefore a need exists which alleviates the disadvantages of using either silicone or fluoropolymer for cell culture bags alone.